Study: California Mandated Later Start Times Improved Sleep, Test Scores

California became the first state in the country to mandate later start times for middle and high schools in 2022. Four years later, new research is providing an early look at what happened after schools made the change.

A new National Bureau of Economic Research working paper examined the effects of California Senate Bill 328, which requires most middle schools to begin no earlier than 8 a.m. and high schools no earlier than 8:30 a.m.

Researchers found improvements in student sleep and academic performance following implementation of the law, with some mental health improvements among certain groups of students.

The statewide mandate also required districts to make operational changes involving transportation, athletics, family schedules, and other areas. California's experience provides an opportunity to examine both the outcomes associated with later start times and how districts implemented the requirement.

California Became the First State to Mandate Later Start Times

California lawmakers approved SB 328 in 2019, and districts were required to comply by July 1, 2022, or when their existing collective bargaining agreements expired, whichever came later.

The law generally requires middle schools to begin no earlier than 8 a.m. and high schools no earlier than 8:30 a.m., although rural districts are exempt.

Researchers noted that approximately 80% of responding non-rural high school districts reported changing their schedules in response to the law.

Unlike previous studies examining districts that voluntarily moved their start times, California's statewide policy also required other systems to adjust. Athletic schedules, transportation systems, parental work routines, and neighboring school districts all operate around school schedules, the researchers noted. A statewide mandate can therefore produce changes that a single district acting independently may not be able to make.

Students Got More Sleep After Start Times Changed

Researchers found an increase in student sleep following implementation of the law. The share of students getting at least eight hours of sleep increased by 3.6 percentage points, or 13% relative to the previous average. The share getting more than seven hours increased by 7%. Researchers also found that students were substantially less likely to be awake early in the morning after the mandate took effect.

Among adolescents ages 15 to 18, researchers estimated total sleep increased by approximately 43 minutes. Although bedtimes shifted somewhat later, wake-up times shifted enough to produce an overall increase in sleep.

The effects extended beyond the students directly covered by the mandate. Researchers found younger children in affected households also woke later and slept longer, which they said may reflect changes in siblings' or parents' routines.

Mental Health Findings Varied Among Students

The researchers also examined whether the additional sleep was associated with changes in student mental health. Across students overall, the mental health findings were less definitive. The study found a modest decline in reported difficulty concentrating, while reductions in sadness or hopelessness and suicidal ideation were not statistically significant across the full sample.

However, researchers found larger changes among some groups. Boys, who experienced some of the largest increases in sleep, showed statistically significant reductions in sadness or hopelessness and suicidal ideation, as well as difficulty concentrating. Hispanic students, who experienced particularly large shifts in sleep timing, also reported significant reductions in difficulty concentrating.

Researchers said the pattern was consistent with a relationship in which groups experiencing larger sleep improvements also experienced larger mental health improvements.

Academic Gains Grew Over Time

Academic performance also improved following implementation of the mandate. Researchers found gains in eighth-grade math and English scores, with the largest improvements among Hispanic and economically disadvantaged students.

The academic gains increased over time. Using California Department of Education data, researchers found that improvements in math, English, and science performance increased between 2023 and 2025 as students spent more time under the later schedules.

The study also identified a decline in high school dropout rates by 2025, although the researchers cautioned that the dropout finding should be interpreted carefully because of trends that existed before the policy took effect.

How a Statewide Mandate Differs From District-Level Changes

Previous research on later start times has largely examined individual districts that voluntarily made the change. Those districts may have been especially motivated or had the resources necessary to address transportation, athletics, family schedules, and other complications.

A statewide mandate changes those dynamics. The researchers point out that when one district independently changes its schedule, athletic leagues may continue holding games at their existing times, neighboring districts may operate on different schedules, transportation systems may retain existing timetables, and parents' work schedules remain unchanged.

When districts across a state change simultaneously, some of those surrounding systems may adjust as well. The study's authors describe SB 328 as an opportunity to examine not simply whether later start times work in districts that choose them, but what happens when the policy is implemented across a much larger and more varied group of schools.

Implementation Resources Matter

The resources and technical assistance available to districts also varied as schools adjusted to the new start-time requirements. San Francisco Unified School District, for example, worked with operations experts from the Yale School of Management, Georgia Tech, and Northwestern University to redesign its transportation system, EdSource reports. With more than 120 schools and 18 different start times, the effort generated approximately 1,000 feasible bus schedules and reportedly saved the district about $5 million.

Not all districts had access to the same level of outside assistance. Advocates for later start times have argued that the state could have provided more support as districts worked through transportation and other logistical issues.

Similar implementation questions have emerged with school safety mandates. At least 13 states have enacted Alyssa's Law or related legislation addressing school panic alert and emergency response systems. In Texas, where silent panic alert technology is required in every classroom, Deer Park ISD provides annual staff training, incorporates its wearable alert system into emergency drills, and has procedures for accidental activations. The district also experienced problems with some location sensors during its first year of implementation that were later addressed.

Other requirements are just beginning to take effect. As of Sept. 1, West Virginia county school systems must create standardized school mapping data that can be shared with law enforcement, fire departments, and emergency medical services. The information must be verified through an on-site walkthrough and compatible with software already used by public safety agencies.

Staffing requirements present different challenges. Florida's Guardian Program is one option districts can use to meet the state's requirement for armed security on public school campuses, while Texas districts have reported difficulties meeting armed security requirements because of funding and the availability of qualified personnel.

California's later-start-time law raises some of the same implementation questions. While the new research provides evidence about student outcomes, experiences from school safety leaders offer additional insight into what changing start times can look like in practice.

What School Safety Leaders Say About Later Start Times

Experiences shared by school safety leaders suggest the effects of changing start times can vary by district and may introduce challenges that extend beyond student sleep.

One NCSSD member who previously worked for a Texas district said the district moved elementary start times earlier while shifting secondary schools later. The change created complications involving athletics, student work schedules, and transportation.

Athletes sometimes had to leave school early for home and away games, resulting in additional missed class time. The member also said the earlier elementary schedule meant younger students were waiting for buses earlier in the morning, sometimes in the dark and without adult supervision.

The member said students also appeared to adjust their bedtimes to the later schedule and that they did not observe noticeable changes in high school student well-being, attendance, behavior, or school climate following the change.

A school safety leader in northern Washington described a similar concern. One of the region's largest districts had previously moved school start times later, including an 8:45 a.m. start, but is now planning to shift middle school start times to 7:30 a.m. next year, according to the member.

District officials have said students did not ultimately get more sleep after the previous change because they stayed up later at night, the member said.

Those experiences differ from the findings in California, where researchers found that although bedtimes shifted somewhat later, students still got more sleep because they were waking up later.

The differing experiences also raise the question of whether the outcomes seen under California's statewide mandate would be the same for districts making similar changes under different local conditions.